Method and apparatus for transmitting/receiving audio/video contents in wireless access networks

ABSTRACT

Disclosed are method and apparatus for transmitting/receiving audio/video content data in wireless access networks. The method comprises the steps of: encoding the audio/video content data into a basic stream having a first level of quality and an advanced stream, combination of the basic stream and the advanced stream has a second level of quality higher than the first level of quality; and transmitting the basic stream and the advanced stream with a first power and a second power lower than the first power on antennas, respectively. With the method and apparatus of the invention, the low SINR users are able to maintain the low data rate receiving the basic stream and the high SINR user can receive both the basic stream and advanced stream from two logical channels.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for transmitting/receivingaudio/video contents in wireless access networks and an apparatusthereof, which are capable of enhancing the data rate of high SINR usersand maintaining the data rate of low SINR users by combining spatialmultiplexing and layered source coding together.

2. Description of Prior Art

In wireless access networks, multimedia broadcast and multicast serviceshave been paid lots of attention. Users are able to watch online videoor audio programs from the networks and it also brings increasingrevenues for telecom operators including fixed and mobile operators.Limited by the wireless propagation environments, at the receiverdifferent users usually have different signal interference noise ratios(SINR) and different achievable data rates. To transfer the same volumeof data to users with different SINR in a cell, the traditional methodswere proposed by expanding the operating channel bandwidth, but it willresult in low resource utilization. To guarantee each user to enjoy theprogram fairly, the lowest achievable data rate has to be adopted todeliver broadcasting and multicasting services to all users.

The best existing solution to this problem is the layered modulationcombined with source coding. By utilizing source coding techniques, theoriginal video or audio information is encoded into two differentquality-level streams: basic stream and advanced stream. In themodulation phase, each modulation constellation of the basic stream isthe center of the constellation in each quadrant of the advanced one.Coded bits of basic stream and advanced stream are modulated on theconstellation with larger Euclidean and smaller Euclidean distance,respectively. If the user terminal has high enough SINR, it willdemodulate the coded bits carried by constellation with both largerEuclidean and smaller Euclidean distance; if the user has low SINR, thecoded bits carried by constellation with larger Euclidean distance canbe demodulated.

However this method has the disadvantages as follows. It requires largemodification effort at PHY and MAC layer in the system, and cannot bedirectly applied to existing systems. The demodulation at receiver ismuch more complicated than traditional demodulation.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method and apparatus foradvanced layered modulation and coding by combining multiple antennastechniques and layered source coding. By using this method and apparatusof the invention broadcast and multicasting services in the wirelessbroadband access networks can be achieved efficiently.

In one aspect of the invention, there is provided a method fortransmitting an audio/video content data comprising the steps of:encoding the audio/video content data into a basic stream having a firstlevel of quality and an advanced stream, combination of the basic streamand the advanced stream has a second level of quality higher than thefirst level of quality; and transmitting the basic stream and theadvanced stream with a first power and a second power lower than thefirst power on antennas, respectively.

In another aspect of the invention, there is provided a method forreceiving an audio/video content data, wherein the audio/video contentdata are encoded into a basic stream having a first level of quality andan advanced stream, combination of the basic stream and the advancedstream has a second level of quality higher than the first level ofquality, the method comprises the steps of: applying a MIMO detectionalgorithm to the received signals to generate at least one stream; andrecovering the audio/video content data based on only one stream or ontwo streams.

In still another aspect of the invention, there is provided an apparatusfor transmitting an audio/video content data comprising: an encoder forencoding the audio/video content data into a basic stream having a firstlevel of quality and an advanced stream, combination of the basic streamand the advanced stream has a second level of quality higher than thefirst level of quality; and a transmitting means for transmitting thebasic stream and the advanced stream with a first power and a secondpower lower than the first power on antennas, respectively.

In still another aspect of the invention, there is provided an apparatusfor receiving an audio/video content data, wherein the audio/videocontent data are encoded into a basic stream having a first level ofquality and an advanced stream, combination of the basic stream and theadvanced stream has a second level of quality higher than the firstlevel of quality, the apparatus comprises: a MIMO detector for applyinga MIMO detection algorithm to the received signals to generate at leastone stream; and a source decoder for recovering the audio/video contentdata based on only one stream or on two streams.

The proposed method and apparatus will enhance the data rate of highSINR users and maintains the data rate of low SINR users by combiningspatial multiplexing and layered source coding together.

In this way, the low SINR users are able to maintain the low data ratereceiving the basic stream and the high SINR user can receive both thebasic stream and advanced stream from two logical channels.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic illustration of layered source coding combinedwith spatial multiplexing;

FIG. 2 shows a transmitter structure according to an embodiment of thepresent invention;

FIG. 3 shows a receiver structure according to an embodiment of thepresent invention;

FIG. 4 shows a flow chart illustrating a method for transmittingaudio/video content data according to an embodiment of the presentinvention; and

FIG. 5 shows a flow chart illustrating a method for receivingaudio/video content data according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic illustration of layered source coding combinedwith spatial multiplexing. As shown in FIG. 1, by using the moderncoding methods, it could provide several different quality-levels ofvideo or audio programs. Generally, a source encoder at a base stationBS can encode the original video or audio information into two streams,one is called basic stream, and the other is called advanced stream.

Compared with SISO systems, MIMO system as shown in FIG. 1 can providearray gain and spatial multiplexing gain. By assigning differenttransmit powers on two transmit antennas Tx1 and Tx2, the antenna withthe larger power ensures the coverage of a BS and provides low-levelprograms. The antenna with the smaller power has a relatively smallcoverage and provides high-level programs by combining the low-levelprograms. Because of the nonlinear and rapid shrink of the minimumEuclidean distance with the increasing constellations, multiple antennasystems have higher power efficiency than single antenna systems. Whenthe maximum total transmission power remains constant, the multipleantenna design has a better coverage and provides higher-qualityservices.

At the receiver such as a mobile station MS, if the signal of advancedstream is weak, for example the signal quality of the advanced stream islower than a predetermined threshold, only the basic stream is handledand low-quality program is obtained. If the signal of advanced stream isstrong, for example the signal quality of the advanced stream is higherthan a predetermined threshold, both the two streams are combined at thesource decoder, and the high-quality program is obtained.

As shown in FIG. 2, the transmitter according to an embodiment of theinvention comprises a source encoder 10, a first channel encoder 11, asecond channel encoder 12, a first modulator 13, a second modulator 14and two transmit antennas Tx1 and Tx2.

The original video or audio information is fed into the source encoder10. The source encoder encodes the video or audio information into twostreams including a basic stream and an advanced stream. The basicstream corresponds to the audio/video having a lower level of quality,while the combination of basic stream and the advanced streamcorresponds to the video or audio having a higher level of quality.

Both streams are channel coded and then modulated independently. Forexample, the basic stream is channel coded in the first channel encoder11 and the advanced stream is channel coded in the second channelencoder 12. Then, the channel coded stream is modulated in the firstmodulator 13 and the channel coded stream is modulated in the secondmodulator 14. Based spatial multiplexing methods, the two streams aretransmitted on the two antennas Tx1 and Tx2 by using different transmitpowers, respectively. For example, the basic stream is transmitted witha higher transmit power and the advanced stream is transmitted with alower transmit power.

Here the adjustment of transmit power is in accordance with mobilenetwork planning. Firstly P_(A1) is chosen based on the coverageconsiderations, and then considering other factors, such asinterference, power restrictions, etc. to set the value of P_(A2), whichdecides the coverage of high quality-level programs.

As described above, spatial multiplexing methods are applied to transmitthe two quality-level source coding video/audio streams in two logicalchannels, and larger transmit power is allocated for the basic streamthan that for the advanced stream. Each stream is channel coded andmodulated independently. Different channel coding methods, differentcoding rate and different modulations also can be applied to these twostreams.

As shown in FIG. 3, the receiver according to an embodiment of thepresent invention comprises antennas Rx1 and Rx2, a MIMO detector 20, afirst channel decoder 21, a second channel decoder 22 and a sourcedecoder 23.

Based on the received signals on the two receive antennas Rx1 and Rx2,the MIMO detection algorithms can be applied in the MIMO detector 20 togenerate the original transmitted symbols and the two streams are alsoseparated in two logical channels. Both streams are channel decodedindependently in the first channel decoder 21 and the second channeldecoder 22 and fed into the source decoder 23. The source decoder 23will make a decision, whether to recover information based on only thebasic stream or on the combining of these two streams.

For example, the derision indication can be obtained by several methods,e.g. according to the results of the channel information, e.g. receivedSINR. Packet error rate at MAC layer can also be as an indication.

FIG. 4 shows a flow chart illustrating a method for transmittingaudio/video content data according to an embodiment of the presentinvention.

As shown in FIG. 4, at step S101 the original video or audio informationis fed into the source encoder 10 and the source encoder encodes thevideo or audio information into two streams including a basic stream andan advanced stream. As described above, the basic stream corresponds tothe video or audio having a lower level of quality, while thecombination of basic stream and the advanced stream corresponds to thevideo or audio having a higher level of quality.

At step S102, the basic stream is channel coded in the first channelencoder 11 and the advanced stream channel coded in the second channelencoder 12. Then, the channel coded stream is modulated in the firstmodulator 13 and the channel coded stream is modulated in the secondmodulator 14.

At step S103, based spatial multiplexing methods, the two streams aretransmitted on the two antennas Tx1 and Tx2 by using different transmitpowers, respectively. For example, the basic stream is transmitted witha higher transmit power and the advanced stream is transmitted with alower transmit power.

For low quality stream, the higher TX power at one of the two antennasis used to cover the area as large as possible. For high quality stream,the lower TX power at the other antenna to avoid interference tolow-SINR user while achieving spatial multiplexing gain by high SINRusers.

FIG. 5 shows a flow chart illustrating a method for receivingaudio/video content data according to an embodiment of the presentinvention.

As shown in FIG. 5, at step S201, based on the received signals on thetwo receive antennas Rx1 and Rx2, the MIMO detection algorithms can beapplied in the MIMO detector 20 to generate the original transmittedsymbols and the two streams are also separated in two logical channels.

At step S202, both streams are channel decoded independently in thefirst channel decoder 21 and the second channel decoder 22 and fed intothe source decoder 23.

At step S203, the source decoder 23 will make a decision, whether torecover information based on only the basic stream or on the combinationof these two streams. For example, the decision indication can beobtained by several methods, e.g. according to the results of thechannel information. Packet error rate results at MAC layer can also beas an indication.

In this way, the low SINR users are able to maintain the low data ratereceiving the basic stream program and the high SINR user can receiveboth basic and advanced streams program from two logical channels.

In other words, this invention combines advanced layered coding andadvanced multi-antenna technologies. Each user can achieve differentquality-level multimedia broadcast and multicast services, which isdecided by its channel conditions. The realization of such a function isprovided by the high layers, no it is no need to make any modificationto PHY layer of the system, which simplifies the design of system orterminals greatly.

Efficient resource utilization for providing the better multimediabroadcast and multicast services in an adaptive way as follows. Anadaptive mechanism can be applied, that is, automatically choosing modesbetween high-quality programs and basic-quality programs without user'sintervention. The receiver remains low complexity. User quality ofexperience with fairness among users is greatly increased, and betterSINR users enjoy better quality service. Array gain and spatialmultiplexing gain provided by multiple antennas can significantlyimprove the system capacity and power efficiency. Different channelcoding and modulation modes can be applied into the transmission ofbasic stream and advanced stream to meet their different BERrequirements. Basic stream and advanced stream are processedindependently, which is transparent to PHY layer and no PHYmodifications to the existing system are needed.

While the invention has been particularly shown and described withreference to exemplary embodiments thereof, the invention is not limitedto these embodiments, it will be understood by those of ordinary skillin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the claims.

What is claimed is:
 1. A method for transmitting an audio/video contentdata comprising the steps of: encoding the audio/video content data intoa basic stream having a first level of quality and an advanced stream, acombination of the basic stream and the advanced stream having a secondlevel of quality higher than the first level of quality; andtransmitting the basic stream and the advanced stream with a first powerand a second power lower than the first power on antennas, respectively,wherein the second power is set by taking interference and powerrestrictions into consideration.
 2. The method of claim 1, furthercomprising the step of: independently channel coding and modulating thebasic stream and the advanced stream.
 3. The method of claim 1, whereinthe first power is set in accordance with coverage.
 4. A method forreceiving audio/video content data, wherein the audio/video content dataare encoded into a basic stream having a first level of quality and anadvanced stream, a combination of the basic stream and the advancedstream having a second level of quality higher than the first level ofquality, the method comprises the steps of: applying aMultiple-Input-Multiple-Output (MIMO) detection algorithm to receivedsignals to separate the basic stream and advanced stream into twodistinct logical channels; independently channel decoding each stream ina respective channel decoder; and feeding the output of each channeldecoder into a source decoder, wherein the source decoder is configuredto determine whether to recover information based on the basic streamalone or the combination of the two streams.
 5. The method of claim 4,further comprising the step of: independently channel coding anddemodulating two streams.
 6. The method of claim 4, wherein therecovering step is based on the results of channel information.
 7. Themethod claim 4, wherein the recovering step is based on packet errorrate results at MAC layer.
 8. The method of claim 4, wherein two streamsare separated in two different logical channels.
 9. An apparatus fortransmitting an audio/video content data comprising: an encoder forencoding the audio/video content data into a basic stream having a firstlevel of quality and an advanced stream, combination of the basic streamand the advanced stream has a second level of quality higher than thefirst level of quality; and transmitters for transmitting the basicstream and the advanced stream with a first power and a second powerlower than the first power on antennas, respectively, wherein the secondpower is set by taking interference and power restrictions intoconsideration.
 10. The apparatus of claim 9, further comprising firstand second channel encoders and first and second modulators forindependently channel coding and modulating the basic stream and theadvanced stream.
 11. An apparatus for receiving an audio/video contentdata, wherein the audio/video content data are encoded into a basicstream having a first level of quality and an advanced stream, acombination of the basic stream and the advanced stream having a secondlevel of quality higher than the first level of quality, the apparatuscomprises: a Multiple-Input-Multiple-Output (MIMO) detector for applyinga MIMO detection algorithm to received signals to separate the basicstream and advanced stream into two distinct logical channels; first andsecond channel decoders for independently channel decoding each stream;and a source decoder, receiving as inputs the outputs of the first andsecond channel decoders, for recovering the audio/video content databased on only one stream or on two streams.
 12. The apparatus of claim11, further comprising first and second channel decoders forindependently channel decoding two streams.